The present invention relates to a method for producing an organic electroluminescent device having a plurality of luminescent regions of organic electroluminescent elements on one substrate, which can be used in such fields as display elements, flat panel displays, back lights and the interior.
In recent years, organic electroluminescent elements attract attention as new luminescent elements. In this element, the holes injected from an anode and the electrons injected from a cathode are recombined in an organic emitting layer held between both the electrodes, and C. W. Tang et al. of Kodak demonstrated for the first time that it emitted light at a high luminance at a low voltage (App. Phys. Lett. 51 (12) 21, p. 913, 1987).
FIG. 37 is a sectional view showing a typical structure of an organic electroluminescent element. A hole transport layer 5, an organic emitting layer 6 and second electrodes (cathodes) 8 are laminated on transparent first electrodes (anodes) 2 formed on a glass substrate 1, and the light emitted due to the drive by a drive source 9 is taken outside through the first electrodes and the glass substrate. Such organic electroluminescent elements, with a thin thickness and under low voltage driving, can emit light at a high luminance and also allow multicolored luminescence by selecting organic luminescent materials. Their application as electroluminescent devices such as display elements and displays is being actively studied.
In these case, for example, in a passive matrix type color display as shown in FIGS. 1 to 3, a technique for highly precisely patterning at least an organic emitting layer and second electrodes is needed, and in an active matrix type color display, a technique for highly precisely patterning at least an organic emitting layer is needed.
For such fine patterning, photolithography is conventionally used as a wet process. Japanese Patent Laid-Open (Kokai) No. Hei6-234969 discloses a technique for obtaining an element to allow application of photolithography by devising an organic material.
As methods for patterning the second electrodes without using any wet process, Japanese Patent Laid-Open (Kokai) Nos. Hei5-275172 and Hei8-315981 disclose partition techniques. In the technique of Japanese Patent Laid-Open (Kokai) No. Hei5-275172, partitions are arranged with intervals on a substrate, and an electrodes material is vapor-deposited on the substrate in an oblique direction. In the technique of Japanese Patent Laid-Open (Kokai) No. Hei8-315981, partitions with overhangs are formed on a substrate, and an electrode material is vapor-deposited on the substrate from within an angle range with the vertical direction as the center.
The conventional masking methods are general patterning methods without using any wet process. In these methods, a shadow mask is arranged before a substrate, and a deposit is vapor-deposited through apertures for patterning.
As a fine patterning method by masking, Japanese Patent Laid-Open (Kokai) No. Hei9-115672 discloses a masking technique using a shadow mask with a single layer structure. In this method, a shadow mask wider in mask portion than in aperture width is used for patterning an organic thin film layer and second electrodes for each luminescent color, to allow the production of a practical pitch passive matrix type color display.
On the other hand, though not relating to the method for producing an organic electroluminescent device, Japanese Patent Publication (Kokoku) No. Sho63-38421 discloses a technique for forming a wiring pattern by using a shadow mask with a laminate structure. In this method, a two-layer shadow mask consisting of meshes and a foil with a pattern formed, either of which is a magnetic material, is kept in contact with a substrate by a magnet, for vapor deposition. Since the meshes inhibit the deformation of apertures, a complicated wiring pattern such as a cyclic circuit portion and a curved thin circuit portion can be formed.
However, the above mentioned conventional methods have the following problems.
According to said photolithographic method, since the organic thin film layer used as a component of an organic electroluminescent element is generally poor in the durability against water, organic solvents and chemical solutions, the performance of the organic electroluminescent element is remarkably degraded. Furthermore, to obtain an organic electroluminescent element allowing the application of a wet process, the materials used are limited.
According to the partition methods, since patterning is achieved by using the shadows of the deposit formed by partitions, highly precise patterning cannot be achieved when vapor deposition is effected at various angles or when vapor strays behind the partitions in a large quantity. So, these methods are not suitable for larger substrate areas, higher vapor deposition rates or more highly precise patterning. Furthermore, since regions free from the second electrodes called dead spaces corresponding to the shadows of the deposit exist on the organic thin film layer, the organic electroluminescent element tends to be deteriorated by the invasion of water, etc. from there. Moreover, it is not easy to stably form partitions with a large sectional aspect ratio and specially formed partitions with overhangs on the entire surface of the substrate.
In the conventional masking methods, the vapor strays due to the poor contact between the substrate and the shadow mask. Especially when a shadow mask extremely narrow in the mask portion compared to the apertures is used, for example, for patterning second electrodes formed in stripes, the apertures can be deformed due to insufficient strength of the shadow mask. So, it is difficult to highly precisely achieve the fine patterning in sub-millimeter ranges required for displays, etc.
In the masking method using a shadow mask with a single layer structure, though the mask portion is relatively wide, the problem that the apertures are deformed cannot be solved, and patterning at high accuracy cannot be achieved yet. Furthermore, since the organic thin film layer and the second electrodes are laminated in the same flat form, a plurality of electrode material evaporation steps are necessary for forming the second electrodes, and in addition, the element obtained can be applied only as a display structure in which the second electrodes can function as a data line.
The masking method using a shadow mask with a laminate structure cannot be applied for forming a fine pattern of sub-millimeter ranges since the conventional wiring patterns are generally formed in millimeter ranges. Furthermore, since a shadow mask prepared by placing a patterned foil on highly rough meshes is used, the shadow mask is not sufficient in flatness or accuracy, and it is difficult to highly precisely achieve a fine pattern disadvantageously. Furthermore, since this method forcibly keeps the shadow mask in contact with the substrate by a magnet, the shadow mask easily flaws the organic thin film layer when the organic thin film layer on which the second electrodes are formed is very soft compared to a ceramic substrate, etc. So, since an undesirable accident such as shortcircuiting between the first electrodes and the second electrodes can occur, this method cannot be applied for patterning in an organic electroluminescent device.
As described above, according to the prior arts, it is difficult to highly precisely and stably achieve the fine patterning necessary for production of an organic electroluminescent device, without damaging the organic thin film layer.
The object of the present invention is to solve the above problems by providing a method for producing an organic electroluminescent device which allows highly precise fine patterning under various vapor deposition conditions without degrading the properties of the organic electroluminescent elements and can achieve high stability by a relatively simple process without limiting the structure of the electroluminescent device.